N-hydrocarbylthiophosphoric triamides are known to be effective urease inhibitors for use with urea-based fertilizer compositions. See, for example, U.S. Pat. No. 4,530,714 to J. F. Kolc, et al.
Known procedures for preparing such triamides involve operations in which N-hydrocarbylaminothiophosphoryl dichloride (also known as N-hydrocarbylthiophoramidic dichloride) is formed in a first reaction, recovered, and often purified. In a second reaction, the N-hydrocarbylaminothiophosphoryl dichloride is reacted with ammonia to produce a slurry from which co-product ammonium chloride is separated by filtration. See for example, U.S. Pat. No. 4,530,714.
In commonly-owned copending U.S. applications Ser. Nos. 08/786,396 now U.S. Pat. No. 5,770,771, 08/786,535, and 08/785,104, all filed Jan. 21, 1997,--all disclosures of which are incorporated herein in toto by reference--new, highly advantageous process technology is described for co-producing N-hydrocarbylthiophosphoric triamides and aqueous ammoniate solutions. These ammoniate co-product solutions formed in the processing and are chiefly composed of ammonia and ammonium chloride.
While solutions of ammonia and ammonium chloride made from essentially pure ammonia and ammonium chloride do not cause significant ferrous metal corrosion, it has been found that aqueous ammoniate solutions made in accordance with some of the process technology of the aforesaid applications do tend to cause such corrosion, at least in the case of mild steel. It appears therefore that trace amounts of impurities carried over from the processing is responsible for such corrosion, and since the processing typically involves use of thiophosphoryl chloride (PSCl.sub.3) as an initial starting material, it is reasonable to believe that trace amounts of some currently unidentified sulfur-containing impurities are the cause of the corrosion.
A very desirable contribution to the art would be the discovery of an effective way of inhibiting such corrosion without at the same time requiring use of expensive and/or time-consuming purification procedures.
This invention is deemed to have fulfilled this need.